[MAINT] remove code climate and update badges

[Remi-Gau]

• remove code climate config
• update badges in README
• update links to legacy validator in README

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.70%. Comparing base (b8cb5f9) to head (42aed00). Report is 7 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2190 +/- ## ======================================= Coverage 85.70% 85.70% ======================================= Files 91 91 Lines 3784 3784 Branches 1221 1221 ======================================= Hits 3243 3243 Misses 455 455 Partials 86 86 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.